In general, gas phase synthesis is an efficient way to generate relatively pure particles. Whether plasma, laser pyrolysis, or some other method, a set of precursor gases is flowed into a reaction zone where atoms and/or molecules in the set of precursor first gases ionize and then nucleate. Once present, the nucleated particles will tend to coagulate into soft particle agglomerates, and if enough energy is present, to sinter into hard agglomerates. However, in practice, these agglomerates will tend to clog pumps, block filters, and coat just about any surface to which they come in contact.
For example, a common type of particle collection apparatus is known as a baghouse. Using a fabric bag to filtrate and separate the particles and agglomerates, the baghouse provides a surface on which dust particulates collect through inertial collection, Brownian movement, and electrostatic forces. The fabric bags may be of woven or felted cotton, synthetic, or glass-fiber material in either a tube or envelope shape.
Inertial collection involves the striking of particles on cloth fibers placed perpendicular to the gas-flow (direction instead of changing direction with the gas stream). Browning movement involves probability of contact between the particles and surfaces in the particle collection apparatus because of the diffusion of particles. And electrostatic forces involve the presence of an electrostatic charge on both the particles and the fabric filter in order to increase particle capture.
However, these particle collection mechanisms also tend to result in the formation of particle agglomerate caking on internal particle collection apparatus surfaces, and in particular on the fabric filter, which increases the resistance to gas flow thus back pressure on the vacuum pump. Thus, the filter must be cleaned periodically, often requiring gas phase synthesis apparatus to be taken offline, which may substantially reduce the overall production rate.
In view of the foregoing, there are desired methods of improved methods and apparatus for the continuous in situ collection of particles.